Water from the Basement of Time

By Cynthia L. McVey

If one could have looked at Mars from space
more than three billion years ago, it would have
appeared as a pale blue dot, or a checkerboard
of land with small bodies of water scattered
around. Playing a large role in uncovering Mars’
mysterious metamorphosis into the Red Planet is
John Grotzinger ’79, Sc.D. ’13, mission leader and
project scientist for the Mars Science Laboratory.

The Curiosity rover—a self-contained science
laboratory about the size of a Mini Cooper—was
sent to Mars last year on a mission to find evidence
that the planet could have supported microbial life.
A little more than six months after it landed, it sent
back evidence of a habitable environment.

“We first got a sense that we were headed in the right direction
with the rover when we discovered an ancient streambed very early in
the mission, after only a month of exploration,” explains Grotzinger.
“We decided to follow the course of that ancient stream and it led us
to an ancient lake—long since vanished—which preserved evidence of
a formerly habitable environment.”

He explains the ancient water would have had abundant chemical
nutrients and been relatively fresh, with low salinity and not acidic—
drinkable by human standards.

“It’s very analogous to what would be a pond or shallow lake on
Earth. The lake may have been ephemeral, meaning it might have
dried up from time to time; we can’t tell for sure. But it was wet
long enough to cause a series of chemical reactions that would have
supported microbial life if it had ever originated on Mars,”
he says.

Scientists have thought that water once flowed on Mars
since Mariner 9 did a flyby of the planet in the late 1960s.
The discovery of sedimentary rock on Mars in 2004
convinced them that not only did it flow, but it may have
supported life.

“Sedimentary rocks very often form in the presence of
water, usually by cementation of loose rock particles to
form a rock. As this happens, the chemical composition
of the water—and any organic materials in the sediment
—can be trapped within the cementing minerals and
preserved for billions of years,” explains Grotzinger.
Ironically, it was conducting research on Seneca Lake as
a student that led him to the career in which he’d discover Mars’ ancient
lake.

“Thirty five years ago as a student at Hobart, I was cruising Lake
Seneca and measuring the salt content of the sediment and water and
trying to imagine how the lake became salty,” he says. “I had no way to
know that someday I’d be asking the same question about a 3.5 billion
year old lake on Mars. But in hindsight these experiences all merge
into one that is bound by the study of waters, including those from the
basement of time.”